This invention relates to gas cells used in spectroscopic analysis. A gas cell confines the gas which is being analyzed; and radiation (infrared) is caused to pass through the confined gas.
Long path infrared cells are widely used for the spectroscopic analysis of gases. Typical applications include the analysis of gases involved in chemical manufacturing processes, monitoring of emissions from combustion sources ranging from automobile engines to toxic waste incinerators, and the detection of hazardous gases in the industrial environment. The most commonly used cells are called "White" cells. The design of these cells minimizes internal gas volume by using multiple radiation passes back and forth through a gas-containing chamber. FIG. 1 shows a typical White cell chamber and optical system.
Such cells have certain practical limitations which limit their utility for many industrial applications. First, the cell diameter is quite large compared to any fittings which might be used for pumping gas into and out of it. Thus, despite the relatively small volume, the total amount of flushing gas required to clean out a sample can be quite large. Second, the alignment of the mirrors in a White cell is very critical, making such a cell difficult to use in harsh industrial applications and, in particular, in applications requiring high temperatures or pressures.
The present invention is intended to provide a gas cell which: (a) avoids the need for mirror adjustments inside the cell; (b) tolerates changes in heat or pressure without affecting alignment; and (c) eliminates gas flow problems in filling and emptying the cell.